The question was deleted. I answer regardless.

There is probably a contamination of two different forms.

1) Bhí a scrudaithe samhraidh á gcríochnú ag Síle.
scrudaithe is plural, so á gcríochn... but críochnú is still singular, so á gcríochnú

lit. "Were her examinations of summer to-their completion by Síle" -> Her summer examinations were being finished by Síle.

2) Bhí a scrudaithe samhraidh críochnaithe ag Síle.
In case you use críochnaithe as a verbal adjective, á is superfluous.

lit. "Were her examinations of summer completed by Síle" -> Síle had finished her summer examinations.

go raibh maith agat a Labhráis...I deleted the question as I thought I had figured it out. However, from your answer, that seems not to be the case.

míle buíochas

Bahahaha

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