wheezing but apparently healthy California rabbit doe

We have a California doe that is about 10 months old and has been making a wheezing noise for about three months now (it developed a couple of weeks after we got her). She otherwise appears healthy - bright eyes, no nasal discharge, good appetite, plenty of energy - and the wheezing sometimes appears to disappear for a time only to reappear again later. Her cage is near that of three other rabbits (two other does and a buck) in our unheated basement, and we haven't heard any of the other rabbits making a similar sound despite being in cages right next to her for a couple of months now (they probably even drank from the same water bottle before we labeled the bottles). Has anyone else had a rabbit like this? Could she pose a threat to two new (pregnant) does we're planning to bring in? We're seriously considering culling her (she's failed to produce any litters yet and we learned her sisters took a while to produce young too), but don't know if we will get around to it before we bring in the two new does. I'd like to keep the new rabbits away from the others - at least a few yards distant - for a couple of weeks at least, but we have limited space in our basement and aren't ready to build an outdoor hutch yet (still working on building better protection for our ducks). Ideally I'd wait to get the two new does, but they're ready now, can't keep (owners will soon be going on vacation), and sound just like what we've been looking for - a proven doe and her daughter already bred to an unrelated buck. So far we've had -no- luck with any of the does we have - one appears to be too old (finally delivered two kits, only one alive) after months of trying, our wheezing doe (no young after two attempts), and one that just turned six months old and is to be bred for the first time this month.

Any thoughts? Suggestions?

if it were me, I would not keep her. firstly she is wheezing which shows she is not strong enough immune system. rabbits just seem to be bad in a way that when they get sick like that they never really get all the way well.
secondly, I don't want rabbits that take a long time to reach maturity. the only reason to keep rabbits that take longer to get breeding is if you have a good natural feeding system in place and they are doing well on it. they aren't being fed pellets and just wont be quite up to the pace of commercially managed and fed rabbits. usually this is fine with this setting anyhow.