Hormones in pregnancy can sometimes affect the outcome of a chemical service.
Definitely perform a skin test 48 hours beforehand even if the client only had a colour done within the last 4-6 weeks.
Generally, I’d rather use bleach and low vol peroxide than a highlift tint and 40vol, whether on a pregnant client or not, but foils will be a safer option than a scalp bleach as you reduce the chances of product getting onto the skin.
Olaplex doesn’t penetrate into the skin, just the hair shaft, so I don’t think it‘s a higher risk for a pregnant woman?