1)
Was it good that she prayed much?
1.
Radak citing R. Meir (in Midrash Shmuel 2:9): Yes. Anyone who prays much is answered.
2.
Radak citing R. Levi (in Midrash Shmuel 2:9): No. "B'Chol Etzev Yihyeh Mosar" (Mishlei 14:23) - because she prayed much, Shmuel's life was shortened. Refer to 1:22:4:1.
2)
What is the meaning of "Shomer Es Piha"?
1.
Rashi: He was waiting for her to stop. This is like "Shamr Es ha'Davar" (Bereishis 37:11), "Lo Sishkmor Al Chatasi" (Iyov 14:16).
2.
Malbim: He wanted to hear what she said. Refer to 1:13:2:1.