Chris
HW Cowes is 00:28 on Sat - 00:42 Portsmouth.
The tide turns around HW Portsmouth -1.5 so you should not have too much tide induced chop at say 23:00.
Having said that, you will get a load of chop around Cowes entrance from all the craft heading home. Once past S Bramble it should get smooth(ish) in light winds.
As Zippy said, wait until the mayhem reduces and then take it slowly.
I have seen how you drive, so she has good reason to be nervous.