She won't come upstairs

My father got a Maine Coon cat off of craigslist, and we've been battling her health problems and we've finally gotten a leg up
However, I'm concerned about this beautiful baby. The lady my dad got the cat from said that she was very good with dogs (which at this point I don't believe a word that lady says, after Bella's health problems!) and she seems to be okay. At night. Our other cat is very affectionate and social, he'll sit in your lap all day if you'd let him. He also retrieves toys like a dog (The two cats get along great btw)

My problem: Bella hides in the basement all day long.
Its very dark and a little damp down there, and very cold during the winter. I'm concerned about her health and eyes. The thing is, Bella comes upstairs at night and is very frisky and social.
She's a gorgeous cat! I feel like I never see her, though!
At night she appears to not care about the dogs (I have a Cocker Spaniel and a German Shepherd) but during the day she hisses at them and won't stay upstairs. I bring her up during the day, and she'll run back down as soon as she gets a chance. She also practically taunts the dogs into chasing her (which I forbid and they're usually pretty good about it) by spitting, hissing, and swatting at them (even when she's clear across the room). She's starting to make my cocker spaniel very nervous when she's upstairs at all, and the more she acts like that, the more I'm afraid my GSD gets that look in her eye (the I'm-going-to-eat-you ifyoudon'tstop look )

Any hints/tips ?? I'm so confused as to why she'll come up at night, but not during the day. And she's awake in the basement, crawling all over our stuff and chewing on cardboard boxes

Until you close the door full time she'll never find other 'safe' places upstairs. And maybe you could keep the dogs behind doors or something for a few hours a day for a while so she has a chance to make the upstairs her own (as well as they have) and to explore, etc. As long as she has access to down, she won't come up. Her nocturnal business is built-in, cat stuff, and maybe the dogs sleep more then allowing her to roam.

Thank you, I appreciate the reply.
The problem is, there isn't a door to close. The basement stairs are wide open from the kitchen. I do have a baby gate, but naturally she can jump right over it.
I'm going to see what a can rig up, I guess

I have a cat who loves the basement too, and on rainy days, that's where she lives- she likes to hunt the occasional lizard or whatever (the whatever makes me want to get a caulking gun and seal the basement up! That's what happens when you live near the woods, though! ) I have another cat who spends her days on the 2nd story, and comes down mainly at night . We've had her since she was 2 weeks old, so who knows?

If you can put up a baby gate or 2 for a "safe room" for her (preferably with at least the litter box, if not her food and water too, and a hidey hole - pop up cat tent, Walmart,) and then not let her into the basement, she might feel safer and have more opportunities to get accustomed to your home . That way, she can see the dogs, smell the dogs, and make faces at the dogs, but they can't get to her . I've picked up a "walk through" (has a gate) pressure mounted (no holes in the walls ) baby gate at a children's consignment sale that works great for that kind of situation, without it being a pain in the hind end to step over . Good luck!

Oh, whoops, I was drawing letters for my DD, and missed that last post of yours. I've seen some advertisments for a cheap door screen, that you can attach to an opening. Maybe that would work?