Bloomers really pleased one old girl no end (9)

'bloomers really' is the definition.
I can't tell whether this defines the answer.

'pleased one old girl no end' is the wordplay.
I cannot quite understand how this works, but
'pleased' could be 'glad' (similar in meaning) and 'glad' is present in the answer.
'one' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'girl' could be 'las' (I've seen this in other clues) and 'las' is found in the answer.
A single letter 'i' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?