Maria doesn't look like much at first glance, but she is a very powerful ally; even in single player. She's basically only costs a single resource since she pays herself back a card. Occasionally she will also be free by drawing into a 2 resource card. And for that cost of 1 resource she can remove 4 threat from the table over 2 turns. That's amazing for the cost. She's a great chump block character if you only need 2 threat removed as well.
Not to mention, that in multiplayer she hands resources and options for your entire team of heroes when she hits the field. Your teammates will thank you. She will see play for a long time to come as a powerful low-cost ally.