Couple of questions here, a) how long do you plant to stay, but not settle? b) does she need/want to work during this time. c) how long have you been married?
If she is staying less then six months, has no intent to settle and will not work she just needs to go to the UK with her passport. You can apply for a visitors visa ahead of time, but that is totally unecessary, especially given you circumstances.
If she intends to work, you are probablly best going for a normal Spousal visa. Even though that is a settlement visa, it doesn't mean you are "stuck" there permently. It just means you have the opportunity to reside in the UK, if you wish.