It comes down to five things (in general; not specific to WM & attention, but inclusive of):
1. Diet - Eat reasonably well.
2. Physical Exercise - Can be as simple as walking around the neighborhood; just stay active.
3. Stress Relief - Stress wears you down; get zen when you can.
4. Socialization - Just being around other people helps you stay sharp.
5. Brain Exercise - Different and varied challenges. Crosswords, puzzles, board games, etc. all help. Something that's complex and engages your long-term planning engine is great: she likes strategy games (like Starcraft or Age of Empires). Basically, find ways to put your brain to work. And like physical exercise, variance is key.
The problem with Lumosity and #5 is that any "improvement" you see isn't improvement in mental acuity, but efficiencies in repetition.