not sure about the squeak. Are you using Aspen shavings, or chips, and what grade are you using? I ask because aspen, like many other substrates can get ingested or stuck in the mouth. Not sure if it would warrant squeaking but it might be something to consider. Check her mouth for shavings and mucus.
URI's can sound squeaky but usually its more wheezy. My boas had a URI and sounded squeaky/whistle-y because tehir nostrals were plugged with mucas. I would up her warm temps and check her ambient temps. 88 sounds low for a UTH. Is your UTH your only source of heat? Do you mist/ what is your humidity like? During the winter and spring months, high humidity and low temps are one of the leading causes of URI's. A lot of times you can clear up a URI by raising the temps and cutting back on misting.
If your still having problems you should see a vet. I know they can be pricey but my opinion is based solely on my own experience, where as a vet is qualified to make an actual diagnosis.
Check those things out, and let me know so I can give you better suggestions.
Cheers,
Chris.