Hello,
Yes,it's still a chapel,my mother is a member there,she could possibly know of your Aunt or her family,if she did'nt,she would probably know where to find this information.The 3 horseshoes is now a residential house.To find Frondeg on the map consult Ordnance Survey Sheet 146,on the B4337 between Cribyn and Llanwnen you will see MS [mile stone] marked,just after the road crosses Nant Mynach [the boundary between Llanfihangel Ystrad and Lampeter Parishes by the way].Frondeg is in the small woodland section marked on the map.
Regards,David