to buy herself some new clothes?

[keannu]

What do you mean by "was to" in the following? Does it mean "come to buy" or "come to be able to buy" or "was scheduled to buy"?
"be to do something" always has lots of meanings, so it's confusing.

ex)...Her aunt gave her some money. Mary was to buy herself some new clothes with Aunt Barbara's help and advice. A miracle!....

 

[Rover_KE]

The money was earmarked for new clothes.

Mary could not spend it on anything else.

Rover

 

[keannu]

The money was earmarked for new clothes.

Mary could not spend it on anything else.

Rover

So does it mean be able to or come to do something?

 

[Raymott]

So does it mean be able to or come to do something?

It means, as you say, "was scheduled to buy". I wouldn't put it that way, but you understand it. In this case, it also means "was obliged to buy".

"be to do something" always has lots of meanings, so it's confusing.
I'm not sure I'd agree with that. It always has a basic meaning:
"A was to do B" = "It was planned, or expected, that A would do B."
"A is to do B" = "It is planned, or expected, that A will do B."

"Mary was to buy herself some new clothes."
"It was expected/planned/understood that Mary would buy some new clothes."