Next time you're alone with her, put your arms around her shoulder casually and say with some sort of surprise "Wow, you really have a lot of tension on your right/or left shoulder. When last did you get a massage?"
Her: Really? Yeah, I've been feeling tense in this region ... blah blah blah blah
Meanwhile you should be massaging said shoulder
You: You know what? Move
And you push her face down onto the couch or bed and start to massage her shoulders. Note, you need to say this like someone who knows what he's doing, otherwise it'll be obvious you're just doing it to get sex. It'll be good to have a backup story of how you learnt massage when you were into sports or something.
From there, massage and slowly work your way down, when it's obvious she's enjoying it, start kissing her neck, turn her head, kiss her, and let the rest take care of itself.
PS: This has worked twice for me
