Tinahely proved too strong for the Westmeath winners.
Milltown have missed out on the chance to reach a provincial decider in the Ladies Football Championship.
The Westmeath champions were beaten by Wicklow's Tinahely by 3-9 to 0-10 in their semi-final yesterday.
Ciara Byrne found the net twice while Aobha Harmon added a third goal to book their side's place in the Leinster final.
They will take on reigning champions Kilmacud Crokes in the decider after they defeated Meath's Dunshaughlin 2-9 to 0-5 in their clash.
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