Deductible is how much you have to pay out of pocket before insurance kicks in on bigger things. Often, visits are not something you have to worry about with deductible, but procedures like tests (blood tests, ultrasounds, that sort of thing) or hospital visits often require them. I'd check the co-pay with the company; your mom is not likely to know if the OT is covered as a standard doc or a specialist, and even if she did, she'd probably not know if the specialist requires a different co-pay or not. I know my insurance did.

As for the visit itself, the evaluation (for me) included a longish questionnaire and a few exercises that included keeping my eyes closed while doing different tasks. That's how I found out that I don't know what my body position is unless I see it. I had no idea that I depended on my vision so much. And you're likely to find out some interesting things, as well. I imagine that most OT's have their own variations and may do more physical tests, but I never felt unsafe while I was doing it. Since the OT was forwarned, she did a really good job of keeping me from the middle of the hustle and bustle (I'm very sound defensive, so the noise drives me crazy).

Let us know what happens!