Sisters at heart
It was partly infuriating that the quarians went to war with the geth in the middle of the war with the Reapers. Not only did Shepard have the worry about the Reapers, she now had the worry about the geth wiping out the entire quarian race before she could recruit them.
The admirals needed her help. The geth were under Reaper control which made them significantly stronger. They did however; find the signal which was emitting from a geth dreadnought. Disabling the signal would help immensely.
And who else would know how to disable the signal other than Tali'Zorah vas Normandy. The energetic, young quarian had return to provide aid. Shepard was glad she was back.
In her heart, Tali was a sister to her and it felt right to have her around again.