I don't think that there is anything wrong with wishing her Happy Mothers' Day. Just keep it polite and to the point. Don't use it as an opportunity to engage in another R discussion or to ask her questions about what she plans to do or talk about how much you miss her etc. When you limit contact you are not being rude or obnoxious. You are just keeping a healthy distance to enable yourself to heal. You are adopting a new modus operandi...never rude, never cruel but more business-like as you operate at an arms' length. There may be times when you need to let go some "truth darts" but you will learn to tell when.
As you ACCEPT living with this "space" between you, you will be able to judge for yourself the how to deal with things like wishing happy birthday, mothers' day etc.
