Buy a critter keeper a desk lamp and make your own filter. Make sure you have live plants if you don't get a filter
How dark is her bedroom exactly? Bettas are low light fish, and as long as it's not constantly pitch dark, a betta would be comfortable in dim light. If it's too dark, they do make light fixtures for kritter keepers. They're not great, but they work (for the most part), or the desk lamp idea will work. I found a bunch of clip on LED fixtures (with a plug, otherwise you'd eat through batteries every other day) for 99 cents on eBay just this morning when I was looking. Free shipping too.
I have live plants, like a 75 gallon fish tank has live plants....... My water sprite and hornwort, are under water weeds that are worse then ragweed in my opinion. I love them to peaces for it.
I also do have all the tanks my other betta's were in. I have a lamp, that will also heat the water nicely too. So the heater in there with him, would kinda be over doing it lol. ( kept my longest living betta this way.)
I just found space for the little guy in my living room. That is a plus in a half.
Shes sitting on the fence on whether or not she wants one. So Its better safe then sorry speculating now.
Me, If I had the funding and moved into a large house.... I would buy a 75 gallon tank, move the fish I have all ready to it... and name the betta Lord and master over my 34 gallon.
Then when any fry from my swords or platies got big enough put them in with him, till they're ready to be sold.
but then again, If I had the funds, I would own and breed the fish for my own Aquarium store. My home would also be covered in fish tanks... With betta's at least in every room.
But I don't... there for, I can dream.
Crazy fish lady should be a term. Love my little fishy friends.