With the greatest of respect, she worked with him on a daily basis for a number of years so I would say her opinion of him is very relevant. I didn't see the interview but I assume she was asked what sort of person he was and she answered accordingly. If he was nice to her and treated her with respect, then I can't see any real problem with saying that.
Should she be forced to add a caveat that she is "shocked and appaled" by the charges or something along those lines ?
Once again, this. Helen and Brooke (her on screen sister) were both very supportive of Michael Le Vell the last time this all went on (before the charges were dropped).
She would know him pretty well and has worked with him from a young age so of course she would believe he was innocent.