If you look at the User Guide specifications for each mask the P10 is rated at a noise level of 21 dB which is very quiet -- probably quieter than the AirSense machine. The N20 is rated at 24 dB which is still pretty quite but should be based on specifications noticeably higher than the P10. The human ear needs about 3 dB differential to clearly tell if a noise is louder. My experience with my P10 is that I can hear my machine just barely at night, and can't hear my P10 mask, when it is not leaking. My wife now uses the F&P Brevida, and while it is a bit noisier in my subjective opinion, really don't hear it unless the mask is leaking.
So, that begs the question. Could your mask be leaking and the noise is the leaking mask? Or, could you be opening your mouth letting air escape from your mouth? That can be just as loud or louder. For that reason I have been taping my mouth closed for some time now, which eliminates the mouth leaks. My wife denied for a long time that she knows how to keep her mouth closed when sleeping. But, that was not what I was hearing. With SleepyHead and my account the noise she was making, I finally convinced her to try mouth taping. Now, no noise, and SleepyHead shows an amazing improvement in mask leakage -- which was really mouth leakage. If you want to post a SleepyHead Daily Report for a typical night with each mask, I can give you my opinion on whether you may have a leakage problem or not.
And on the mask size, I don't believe there is any difference in the frame of the For Her version, but with a FitPack it does come with the three smallest size cushions including the XS. The head straps may be smaller on the For Her though, and that is probably a good thing, as the headgear on the P10 is weak. If I order replacement headgear for my I will probably get the For Her version. What I have found with a nasal pillow mask is that the biggest size that you can use is the best. It tends to be more comfortable. If too small it can go too far into your nose. My wife has also found when the cushion is too small the mask can restrict flow or even block right off. Did they give you the other sizes to actually try? If so I would try them as that is really the best way to see what works best.
Hope that helps, but keep in mind mask fit and tolerance is critical CPAP issue. I would not get hung up with one model over another -- just pick the one that is comfortable and works for you. If it works, it works! I do think there is a health benefit in using a Nasal or Nasal pillow mask over a full face mask, even if it requires taping your mouth. See this video for some more detail on that aspect.
I definitely hear the noises as well when I am not asleep when I exhale a little bit over the top. The noise created when exhaling feels louder than the slight whistle of the CPAP machine. I am not sure if I am doing something wrong or if nasal pillows (even XS size) are not meant for me. Or could a bigger cushion resolve the noise due to more sealing? I only go the mask with the one cushion for trial...
Actually, I am not sure if the diffuser causes the noise...
For the night I am using a chin strap which also takes care of any noise using the N20.
I used my going to sleep ramp period last night to listen to my AirFit P10 mask. What I heard when I was not breathing in or out was nothing. While I could feel the air purge flow from the mask vents, I could not hear it. However with each breath in or out I could hear a slight air flow sound, especially when I first went to bed, and my breath depth was deeper. However, it got less and less as my air flow in and out reduced to the normal sleeping level. It got to the point where I really could barely hear the flow. Somewhere about that time I fell asleep, so experiment over!
In any case my thoughts are that the noise my P10 mask makes is not the vent, but the air flow velocity through the nasal cones which fit into your nasal passages. And, if that thought is correct, then it stands to follow that the smaller the nose opening, the higher the velocity of air going through it, and the higher the nose level. Go, my guess is that it is the XS size mask insert that may be the source of your higher noise level. My suggestion would be to try a larger insert size if that is an option. I use the large size insert and noise is not an issue for me.