Sack her out with it, rub it all over her, let her sniff it until she's comfortable with it. If she moves away from it just follow her until she stands still just using a relaxed movement. Hold a treat so she drops her head and slip it over her nose, give her the treat when it is on. If its not that easy - Hold it in place as best as you can if she gets nervous until she calms then when she isn't nervous proceed. Praise praise praise. When you are trying to get her used to it or put it on -if she is nervous don't push her, don't stop, but don't force her to let you put it on her nose if she's fighting it. Show her it is okay and no reason to be afraid. Same goes for the mask.
Hope that helps some
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