Harry_the_best
my sister started w/ a chuuchilla and now its near impossible for her to catch one on the catch chuuchilla quest
This is because Chuuchilla is Uncommon, meaning that your sister has 59% chance of successful catch. There is no tips of how to raise the catch rate since 59% is the maximum percentage for Uncommon Mogas. In addition, it is based on luck of whether your sister will be able to capture or not.
I suggest your sister should limit herself with 1 - 3 Starseeds per Moga. If unable to catch the Moga within the limit of the Starseeds, defeat that Moga and move along. It's better to save the Starseeds. In addition, make sure your sister save her Starseeds so she will have enough to catch Mogas and not wasting them.