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In AN 3.86 it is taught that a stream enterer will be born in human and deva realms for a maximum of seven life times:
"[Some,] with the wasting away of the three fetters, are 'one-seed-ers' (ekabijin): After taking rebirth only one more time on the human plane, they will put an end to stress.
"Or, not breaking through to that, not penetrating that, with the wasting away of the three fetters they are 'family-to-family-ers' (kolankola): After transmigrating & wandering on through two or three more families [according to the Commentary, this phrase should be interpreted as 'through two to six more states of becoming'], they will put an end to stress.
"Or, not breaking through to that, not penetrating that, with the wasting away of the three fetters they are 'seven-times-at-most-ers' (sattakkhattuparama): After transmigrating & wandering on among devas & human beings, they will put an end to stress."
In Great Disciples of the Buddha: Their Lives, Their Works, Their Legacy, by Nyaponika Thera it is mentioned that she wasn't a stream enterer at the time of her death. He gives the reason for her birth in hell as:
When Mallika died her twofold transgression-her sexual contact with the dog and her mendacious attempt to free herself from blame-caught up with her and brought about a rebirth in hell.
and later he says,
Although it was a very short-termed sojourn there, one can see that Mallika had not yet attained stream-entry during her life on earth...