Oh my goodness..I'm practically crying reading this post. My daughter had surgery on her lip hemangioma last year at Boston Childrens (sounds very similar to your daughter's hemangioma/ulceration except on the upper lip) and I can only imagine how you must feel right now. If it were me, I would go get a second opinion ASAP. I would email Dr. Levitin with photos on this site or Corinne or Missy to see if there's anyone else in your area. I may be overreacting but I'm just imagining being in your shoes and wanting to see what can be done to remedy the situation.
When my daughter had her surgery last year, the doctor removed some scar tissue from her ulceration and debulked/shaped. She had stitches kind of like a zipper like you mentioned. It never opened at all or had any issues with bleeding, etc. It got very swollen/bruised and was at it's worst at day 2 or 3 maybe and then improved every day after that. It looked really pretty good a week later. The stitches all dissolved on their own (and I believe I remember the doctor telling me that he had stitched it all up on the inside as well.) She had to only have liquids/very soft foods for about a week or so and then softish foods for about a month or so.
I'm not an expert so I don't know if your experience is common or not, but I think you can trust your intuition that something is not right here??? I say, better to be safe than sorry, and get someone else to look at it! Here's some pictures of my daughter's hemangioma. There are some pictures on here from her surgery and what it looked like afterwards.
I am thinking of you and hoping that it all gets better soon. I'm sure it must have been stressful going into the surgery and then even more stressful to have these complications afterwards. Keep us posted. Yes, definitely post some pictures if you can! I'm sure others will chime in here, but that's just my opinion, after being through something similar.