It's all about the spread of literacy! Maudlyn would be deeply odd as a pronunciation nowadays because the vocabulary item 'maudlin' seems unsuitable as a given name. But, it's the same word: MaryMagdalen was shown in floods of tears in religious art to indicate her repentance, and her name later acquired the meaning of weepy and sentimental, probably alcohol-induced. But this didn't exist in the middle ages, when she and her tears would have been taken very seriously.So the original word split two ways: the medieval pronunciation, spelt Maudlin, became the dictionary word with a lower-case m, and the 'name' Magdalen acquired a 'spelling pronunciation' - newly literate people pronounced it as they saw it. (Actually, it's more of an address than a name: Magdalene (often with four syllables) = Woman from Magdala, just as Jesus of Nazareth can be referred to as the Nazarene).
The Oxbridge colleges got their names when the Maudlin pronunciation was the only one in use, and with their everyday use of it plus their respect for tradition they retained it. But it's the same with, say, Gonville and Caius: nobody outside that academic world would ever use 'Keys' as a pronunciation of 'Caius', and when the students there study CaiusCassius we could hear them say 'I'm from Keys and I'm studying KIE-es'; written down it'd be Caius for both.
I think your British Magdalene was from a consciously archaising family! I've certainly never encountered a modern Magdalen(e) who used the Maudlin version, and the contemporary Mauds I've known have been just that: Maud.
That said, here in South Africa we would expect a rather different pronunciation: makh-da-LEEen, with the stressed final syllable having a long E sound followed by a neutral vowel; which is how Afrikaans works.The kh is that throat-clearing sound, and the usual short form is MAKH-da.