The poem doesn't explicitly say that prayer for a mother on earth mingles with heaven. However, the lines you might be thinking of are these:
> "But the beautiful hands that used to caress me,
> And the loving heart that used to bless me,
> Have long since grown cold, and I know they are waiting,
> In that holy place, where the angels are singing."
These lines suggest that the speaker's mother is now in heaven, and the speaker's prayers for her are directed to that heavenly place. The poem explores the speaker's grief for her mother, but also her belief in a loving afterlife.
Here's how the idea of prayer mingling with heaven can be interpreted from the poem:
* The speaker's love and grief for her mother transcends the earthly realm: Her prayers reach out to the heavenly place where her mother now resides.
* The speaker's faith unites earthly sorrow with heavenly hope: The poem speaks to the comforting belief that even in death, love and connection remain.
While the poem doesn't explicitly mention mingling, it implies a connection between the earthly realm of the speaker's grief and the heavenly realm where her mother resides. The speaker's prayers, fueled by love and faith, act as a bridge between these two realms.