This one is an exception to one of the rules about the place of the adjective, usually all past particle taken as adjectives are supposed to go after the noun.

But the exceptions are

• soi-disant
• prétendu
• ledit
• damné
• maudit
• sacré
• foutu
• fichu
• regretté (au sens de défunt)

And expressions:

• dévoué
• estimé
• vénéré
• etc.

Source: Grevisse

So you will say:

ma mère adorée

but

ma vénérée mère

This said, you will also find ma défunte mère and that even sounds more correct to me this way, to be honest.