As for Hagar, she was trapped.  She was a lowly maid servant of Sarah.  Whatever Sarah said, Hagar was compelled to do.  So after Sarah sent Hagar to be a second wife to Abraham--so that Sarah could raise Hagar's child as her own--that's what Hagar had to do.  She was a slave.  She had no voice.

Problem was, Sarah didn't want her around after Hagar gave birth because Hagar taunted Sarah--lording it over her because Sarah couldn't get pregnant. So Sarah wanted her gone and ran her off.  But after awhile, Hagar returned.  She came back under the protection of Abraham.  Abraham loved his only child.  His son Ishmael.  And Sarah had to watch this relationship between Abraham, Hagar, and Ishmael--that she was responsible for--with envy.  Ishmael was a thorn in Sarah's side.  But not as big a thorn as Hagar.  Hagar had given Abraham something that Sarah couldn't.  It hurt.

It's interesting to note that we sometimes do exactly what Sarah did.  God said that Sarah would bear a son, but she didn't believe him.  She laughed at His words.  But seeing the need for an heir, she took matters into her own hands.  She got ahead of God.  She tried to fix the "heir" problem herself--with regrettable outcome.  We also sometimes forget that when there is something we want done, we need to make sure that it is God's plan rather than implementing our own.

When Ishmael was 13 years old, Sarah (to the astonishment of everyone) gave birth to Isaac.  And that's when Sarah went to Abraham and asked him to get rid of Hagar and Ishmael. "Cast out this bondwoman and her son; for the son of this bond woman shall not be an heir with my son."  The Bible says that this was very grievous to Abraham because he loved Ishamael.  But God comforted Abraham and told him that He would make a great nation of Ishmael.

So Abraham gave Hagar provisions and sent her away into the desert.  However, when her water was gone, she was distraught and wept.  But God heard Ishmael's voice and an angel spoke to Hagar.  "Don't fear.  For God has heard your son's voice." God opened her eyes and she saw a well, and gave Ishmael water to drink.  God watched over Ishmael, and he grew, dwelt in the wilderness and became an archer and the father of the Arab nations.  And Hagar?  God had spoken directly to her, through an angel.  And he called her by name.  "What is wrong with you Hagar?  Don't be afraid."  God sees even the most unimportant of us, and knows our names.