Yes you should be concerned about her pulling her stitches out. My cat had to wear one of those Elizabethan Collars because around Day 5 she started pulling on the stitches. I could only take off the collar for her to eat, or to let her play without it when I was able to watch her every second. She even slept in it somehow. It was pitiful. But I kept telling myself that it was only for a short time, about a week. Once her stitches were out, I was very happy to throw that thing away. I advise you to take your cat back to the vet to check on the stitches, and to get one of those collars.

Just re-read your message and realized you already have the Elizabethan Collar. Then yes, you need to keep it on her as much as possible. It'll be hard to look at her with that collar on, but it's only for a short time.

You might want to call your vet and explain what is going on. If your cat can remove the sutures, the vet might want to use staples instead. When we had our calico spayed, she started to remove the sutures, and we took her back to the vet to have the incision cleaned and staples put in. Staples are stronger and have to be removed when the incision is healed, but the removal that we experienced was almost painless and easily done.

The external sutures are nothing to worry about. I don't even put them in because they cause so much discomfort for the pet and stress for the owner. I've said it before, when I had sutures in my back, I removed them in 8 days because they itched so darn much. I was supposed to wait 14 days too. Didn't happen. Vowed that whenever possible, I wouldn't use external sutures. Anyway, the point being, if you don't need them then there's no worries if they disappear.