You can feed unlimited timothy hay and unlimited regular pellets, and your little one will be perfectly OK, or if you really wish, you can add a handful of alfalfa hay, but it is frankly not necessary with good quality pellets (which contain both calcium and protein). Be aware that a handful of alfalfa will serve mum AND all of her babies during the nursing period...
Alfalfa is not a grass, but a legume, so it is important to feed unlimited grass hay, which is what piggy digestion is laid out for. please be aware that some youngsters will pee in their pellet bowl, so it is advisable to not just top up the bowl, but rather feed less more often, so it doesn't spoil.