I’m absolutely not an expert, but I will advise you from previous knowledge (not 100% though). I believe I heard that Guinea Pigs tend to have a faster heart rate than us and breathe quicker also. So I think you should be okay to bathe her/him! Just make sure to monitor your pig and not overdo it with stress. From what I’ve seen, my pigs get very nervous during bath time. The best thing to do is to make sure the water is comfortable (test with your elbow) and make sure you’re in a warm enough room. Also put something to reduce the pig from slipping on whatever surface you’re bathing them on (sink, tub, etc.). I also play some soft anxiety reducing music and make sure to talk to them softly the whole time. Bath time is mildly traumatizing for them, except for the rare pigs who I’ve heard enjoy it, so do it sparingly and only when needed.
Hope this helps!