My filly is too young to be weaned but Mom is struggling....?

I have a filly born 5/6/11 and for being under 2 months old, she is HUGE... Mom doesn't fuss about feeding time but filly is sucking her dry. The baby is eating hay, occasionally sneaks a taste at feed and drinking water well. She's rather independant and loves to "play" with her neighbor (BIG paint gelding) along the fence line. She's far too young to be weaned I think however I'm having trouble with Mom dropping weight. She's got access to green grass, good quality hay and feed... what else can I do other than maybe start helping with milk supplement for filly. Any suggestions or advice is welcome.