We've been to each one 4 or 5 times over the past year. They've each got their pros and cons, though since you don't have kids, it may be different for you. Plenty to do at BB besides Summit Plummet. Lazy River is fun, and there are a number of smaller slides to do there, if she'll do them...Teamboat Springs is a fun family size tube ride, Snow Stormers is fun, Tobbagin Racers is really cool (sliding belly first on mats). Their large pool is much calmer than TL pool. BB has more to do for younger kids, though that won't apply for you.
TL has some really cool slides. She may like Crush 'n' Gusher and the other ones around it. They're not huge drops, but they're really fun...you're in an inner tube and water jets will push you up a small hill and over the next crest. The wave pool there is nuts. The waves are massive and will catch you off guard if you aren't ready for it. It also has other smaller slides and a family size tube ride also.
Frankly, you'll have fun at either one. Get there early, it gets crowded fast.