I'm not seeing any dis-colouration of the glass - the sort that might be due to water staining or some other age related effect - this vase looks quite clean, so I'd agree that the very slightly yellowish tinge is in the glass. This might be because your vase contains either very little or no lead content - I seem to recall we've discussed this before somewhere on the Board, but don't remember where. If you flick the vase does it have that lead glass 'ring'? - if not this might be soda glass, which is known to have a slightly brown/yellow tint, and suggests the vase might be Continental. That centre area looks as if it might be moulded - and is the base flat or depressed?
Assuming cut glass, then those relief diamonds should feel reasonably sharp and not smooth like pressed glass.
Sorry none of this really helps - but it's attractive - tell your Mother to buy only those pieces with labels on