@Dundee67890 This sounds like a really difficult situation. You're made to feel like you can't relax and feel comfortable in your own home when your DSD's there, especially after a week having done what sounds to be a very demanding job. You're made to feel excluded by her who you feel you've tried your hardest to bond with and by your DH that should have your back and should be supporting you through things you're finding difficult, that must hurt, alot.
But I have to implore you, please do not place all your sadness and anger (which you are very valid to be feeling) on the head of your DSD. I say this as a step daughter. My situation is slightly different as I lived with my step father full time (I was also around 6/7 when he entered my life).
First of all, I was a very similar teenager. Kept to my room, rarely speaking to my SF (or even my mother), being scowly, disrespectful, taking in food and drink, extremely untidy in and out of my room, not wanting to spend 'quality time' with family. Although I agree her room sounds revolting but I kind of think it's a good sign that she feels so at home in your place to act like this, and at least it sounds like she joins you for dinner. Whilst others may strongly disagree, in my eyes, yes, that is normal teenage behaviour, especially of someone who has gone through a trauma of their parents splitting and finding new partners. Even if it looks from the outside that the child took a situation like that in their stride, it is undoubtedly a traumatic experience - their life as they know it has been turned upside down. I don't know when your DH and her mother split up but I've read this kind of event can have an effect even on babies, and at least having to get used to a step parent could be a big, overwhelming thing to manage for a child.
I think her mother and to a certain extent your is DH (consciously or subconsciously) are causing a rift in the relationship between you and your DSD. Growing up and especially in my teen years, my mother gave me the impression that I was a burden on my SF, that he judged me if I took any misstep in my behaviour, that he was always fed up with me. Hence I avoided him as much as possible, not speaking to him, kept myself to myself. I enjoyed wallowing in my teenage angst and hating 'the man that took my mother away from me'. Now I'm in my early 30s and I've finally realised my mother's toxicity, I don't believe that was his feelings towards me at all. In fact I remember, I think it was my 13th birthday, that he wrote me a long email (probably too embarrassed to do it in person!) about how the teenage years are going to be tough but he hopes we can get along... I really don't remember it well at all because I was so overwhelmed and embarrassed by this unusally heartfelt gesture that I never acknowledged it and never replied, which I really regret now (I'm trying bring up the courage to talk to him about it one day). I get how he would be reluctant to try and force a relationship after that, perhaps he thought it was 'not his place' to act as a father (my mother was very overbearing!) so he probably reciprocated my taking a step back. I think this is what you're on the verge of doing.
Currently I am not in contact with my mother but the silver lining is that I have a much closer relationship with my SF than I ever have. There is still a long way to go but I feel hopeful that what we're on the same page in wanting to have a better relationship. I know it seems like a long way away and you might not feel like it now, but please remember you could form a loving bond in the future, and you could absolutely bring a lot of value to her life.
I would agree with others that you should restrain yourself in tidying her room - neither she nor your DH should be expecting you to either. I can also understand the impact it has on your mental health to have a room in your home that is so gross! But as you mentioned, it's her private space, and at 17 it's her responsibility, not yours. As a teenager I would only tidy my (frankly, sounds equally as gross) room if I was to have friends or my boyfriend over, and if I didn't, they would definitely call me out on my grossness! My SF never entered or commented on my room (to my knowledge) and my mother rarely did enter, but sometimes would make a (fair!) comment on how gross it is. I didn't pay her any attention of course, and in my case the embarrassment of having my boyfriend comment on it made me change my ways, and in time learnt that a clean room is actually a lot nicer to spend time in. By the way, now I'd say my cleaning and tidying standards are higher than average and can totally relate to the OP's unease at having such a room in her home!
Anyway, one thing I was wondering was what the bathroom situation is like. Does she feel like the bathroom is her space as well? Does she keep her bathroom products there? Did you get her a bin for a room especially for her to dispose of her sanitary products, because that could have sent her a message that she couldn't dispose of her pads in a bin in the shared bathroom, which is where I would have expected people to dispose of their sanitary products. A tiny gesture like that, for a sensitive teenager, could feel like some sort of rejection.
The fact that she knows that you see and clean away her used period pads, I would take it as some sort of communication, a protest or something. I'm not saying it's not gross, but in my opinion that's probably not normal, and so would read into it a bit more?
That thought came to me because I recently read a book, 'The Book You Wish Your Parents Have Read (And Your Children Will Be Glad That You Did' by Phillipa Perry. I would highly recommend the book for you, you don't need to read all of it, just the 2 chapters about Feelings and about 'All behaviour is communication'. The Feelings chapter is useful in general for all relationships and human social interaction, in my view.
The other question mark is about how your DH is acting. Shouting at you or ignoring you when you raise how you feel is not very supportive, but it might help to try and find out why he reacts in this way - perhaps you bringing up the fact that you feel upset triggers his insecurity about being a good dad/spouse? I don't know the dynamics, but if you feel that you have a decent marriage in all other ways, I feel you can get to the bottom of this unsupportiveness and unwillingness to engage somehow and be able to have a frank conversation.
I think it might also help to be open and vulnerable and share how you feel when it comes to the whispering and the exclusion, to both of them. That might be a better approach than going in 'strong' and saying something like 'I won't have this in my house'. Maybe they need to really understand that frankly it makes you very sad. A word of caution, this kind of open heartedness could result in my situation where the step daughter feels utterly embarrassed and overwhelmed if this has not been how you have presented yourself before (or have been presented by your DH and her mother), so it might not work but at least you've tried!
I'm sorry this is a super long response! But I felt that I was quite well positioned in being able to offer some thoughts, having had a step father with whom I didn't have a good relationship with in my teen years, and having just read that book. I also have been learning a lot about childhood trauma and how that can affect children well into teens and adulthood since my husband and I are looking to adopt. In summary, to answer your question 'is this normal?', I'd say it's yes given the circumstances, but I feel there is definitely scope for improvement, especially if you can get your DH to open up a bit and get onside. Good luck and remember, she's a teenager, people grow up, and maybe it's simply a matter of laying low until it's time she's ready to have a respectful, adult relationship with you which could bring you both a lot of joy and value. Keep hopeful!