Hair is going to be pretty key, and of course her body. But if its her jawline for instance, if she has layering that's sort of coming in and the sides it would cover some of that up... a pic would help, though i can understand why you wouldn't slap one up ;)
I think, first of all, to try out all "girly" items and rule out those that don not look good on her. With all I mean: - Long hair, pony tail or hair braid (s) - Nice dress or skirt. - Nice top and showing belly. - Heels - Stockings - Make-up Some experiments should help determine what looks good on her!
As bad as this may sound maybe look for some crossdressing tutorials? Those guys do AMAZING things with their makeup. They look so gorgeous and I get so jealous! Contouring and changes in application may become her best friends :)
When a woman with manlier features wears A LOT of makeup she probably make herself look like a transgenedered person. Use makeup that gives emphasis to her best features. She should also wear clothes that give the illusion of the hourglass shape. I think it's quite modern and feminine.
Try different hair styles and also different fashion styles, you will able to find one that embrace her feminine's side more. Does she wears more make up to look feminine? Maybe when she wears less make up, she could achieve more soft look.