I used to play a Psyker in a campaign and saw that I could put these wards on a set of armour. I was told flat out that I could not do so in that game as they would intefere with my Psyker's ability to use her abilities.

I was never quite sure if this was because:

A - The GM didn't want my character any more powerful than she already was

B - He saw something in a book, and therefore believed that they wouldn't work properly

C - Or he just was doing so based on 'canon' somewhere in the rules

I have not been able to find anywhere in the rules or elsewhere supporting his theory. RAW written does not support it, unless you just use the GM fallback of 'it's that way in my game'.

Before I use the character in another campaign, I would to get other people's opinion on this ruling.

Can a Psyker use the ward on a set of armour without restricting their Psy abilities? If the abilities were to be restricted, then how?

I cannot cite any place to look but I thought I had read that a psyker could get warded armor, just as long as the wards were attuned to them. By attuning the wards they do not affect the psykers abilities.

I would have this be a part of the creation process and require the presence of the psyker in the creation of the wards.

Psykers can absolutely use Hexagrammatic Warded armor, with no penalties or drawbacks for doing so.

There are several items which defend against psychic attacks, which a psyker CANNOT use. For example, the Psy-Jammer on pg 190-191 of Inquisitor's Handbook in the very same section as Hexagrammatic Wards. However, these items specifically and explicitly state that their use is forbidden by psykers.