I would say that this is no different than being examined by a female nurse or doctor. If you are mindful that this is a professional situation and keep your mind on other things, there should be no issue.
My female electrologist has a wide range of hum-drum topics that keeps my mind off of both the discomfort and the overall situation. Over time, I've come relax a little around her. Although I have gotten slightly enlarged during a treatment on occasion, I have never actually gotten a full erection.
She never seems to notice but has said that she is not disturbed when a male client does get an erection -- but is not impressed if a client is obviously trying to get hard or ejaculates. She does have some stories she has shared with me. She has seen it all over the years so any partial erections I've ever gotten are no big deal by comparison.
If you don't worry about it, you should be fine.
Continuing my hair-removal journey after more than five years -- nearly full clearance Brazilian mainly with electrolysis. Now expanding to other areas.