As you have only been dating a few months, I don't think it's long enough for her to be viewing this long-term, even if you are. I do think losing her husband might play a part in that, too, regardless of how long ago.
It's still the honeymoon stage. It's most certainly not long enough, or at the stage to be talking about her Facebook profile picture. When the honeymoon period is over, and the lust dies down, if you both still feel the chemistry, and still enjoy each others company as much as you do now, then you know it's more of a long-haul relationship. However, this is usually a gradual progression where you really get to know someone given 'good time' to see where it leads. You already said she has told you she wants to continue. Isn't that enough at this stage?
Unfortunately, because you are both older, time is against you. However, if this really is a concern for you because of time, I think an important discussion to have with her right now is the one about your comment stating, "there are plenty of other women out there that are interested in a long term relationship and possibly marriage". This comment says a lot, and if you present this to her, you will truly know how she feels and where she stands right now on this matter. She will either stay, or run, but you will know either way.
She does need to know how you feel, as much as you need to know how she feels. You might even be wasting her time. You both may have loads of similarities but want different things, also. She may not want to get married again, or may not be looking as long-term as you. It would only be you wasting your time if you don't ask about these things that are so important to you. Just not the Facebook profile picture.
You have to make decisions and be responsible for your life. Any delay from moving on is ultimately down to you.
I must say that there are some things you have stated that are quite confusing and contradictory, I feel.
You are using statements such as: "I am ok with things how they are. What we have is more than just a few casual dates. It's too soon to ask her for something too serious. I just want to take it to the next level. We both know what we want, I don't wanna date anyone else because I feel she is the one."
However, I think that this may be because you could be so back and forth with your feelings on the whole thing. For a period of time, you're ok and happy with it and where it's going, and then you may be experiencing feelings of doubt and insecurity. I think that's normal, but you might be confusing her too.
Anyway, I wish you all the best with it 😊