If you have the pre-anesthesia blood work done, you should not have a problem with the surgery. There is ALWAYS risk, though, so be aware of that.
The parvo should not be a reason to forego the surgery. Neither should the GI issues.
It will be just as safe as spaying any other dog. The GI tract is not involved at all in the spay process EXCEPT for increased gas following the procedure.
A blood test is the best way to find out if she is a candidate and it's usually the most conclusive.
I am not familiar with laser spays and can only tell you what I have read about it. It is rare in my area so we have not experienced it. However, we do normal spays every day with our rescues so I know all about that. I have even assisted with several. The procedure is done through a small incision in the abdomen. The work is performed, the uterus and ovaries removed and the dog is sewed back up (to make it short and sweet!). Within 24 hours, the dog feels better.
I think that the risks are much greater if you DON'T spay her. You will not only have to tolerate heat behaviors but you will also have the increased risk of mammary, uterine, ovarian and reproductive cancers. You also run the risk of pyometra, a dangerous uterine infection.
I hope that this helps some. If not, feel free to ask more questions.