Hi Cupcake and welcome
You don't mention whether or not your DD is losing weight, but presumably the GP has checked out her growth etc compared to the charts?
When we first sought help (I am ashamed to say that he was over 2 before we realised that we had a problem that we were not going to be able to fix) we were given this booklet here
We then graduated on to this one <a class="break-all" href="https://docs.google.com/viewer?url=www.ndr-uk.org/administrator/components/com_virtuemart/upload/HCSWE_sample_16.2.12_new.pdf&TYPE=PDF&pli=1&chrome=true" rel="nofollow" target="_blank">here
You can get hard copies of these through your HV or dietician at the baby clinic or children's centre or your local health NHS trust's dietician service.
The main messages are that you have to remain completely calm and nonchalant at mealtimes PLUS the idea that calories are king. Variety is a secondary issue. There are lots of good tips in those leaflets and I think that most children will respond to the techniques. The key is staying calm and with hindsight I really do wonder whether our stressing at mealtimes in the first few years didn't just consolidate the problem. So take the chance of using our collective experience and try to get into a calm state about it now. Yes - I know it is easier said than done, but it does get easier with practice.
I think that many children start developing fussy eating habits about 18 onths. The fact that she previously ate well and was using cutlery does make me wonder whether she is just in a phase which she will grow out of if you can back off. I was still having to spoon feed DS at 2, so I am well impressed if your DD was keen enough to eat independently before that, never mind use cutlery!! Anyway if you ignore "bad" behaviour and praise the good stuff, you might find that she comes back to the cutlery in time.
You are also already ahead of us if your DD likes fruit. That is great as if you can get plenty of that into her you are less likely to need to use vitamins and supplements. (see up thread for our list of liquid supplements and fish oils that we hide in a daily smoothie for our DS). If she likes crunchy/crispy things then try to think of high calorie foods in that vein. So you could try giving her Salt n Shake crisps (without the salt) alongside the preferred baby crisps, maybe? Or dry fruit & fibre breakfast cereal without the milk in it? (my DC will only eat it dry as a sort of crunchy snack!) Think about the "acceptable" foods that she likes and then try to get similar stuff so that you can rotate things so that the meals are not always the same. We don't have a great deal of rotation but I do my best. The main thing is that you have to put aside any expectations of variety or homemade stuff or all the things that you think that a "good mum" would do. Nobody has told our DCs about this, so they are not aware that they are expected to appreciate it! 
It never worked for us, but do you think that she might go for food if it was cut into interesting shapes? Or there was a picture on the plate that she had to eat to see?
Try keeping a food diary over a month. You can then try to see if there are sufficient calories going in over a day or a group of days, rather than at a meal. That can be a bit reassuring. DH spends a lot of time looking at calories and protein contents of what we feed DS. It is amazin how much protein is actually in bread, which is lucky as that is mainly what he lives on!
If you try all of that and document what you have done with diaries, if your DD is still difficult after 2, then you will probably be able to convince your GP to get you a referral to see a dietician. If she is constipated he might send you earlier tho? I assume from his comment about it being "your fault" that he might not have realised that she is a resistant eater?
Sorry you are having a hard time. I hope it gets easier for you soon.