No Heat after Matrix

[JustStarting]

I'm just beginning the first time (for me and them) breeding process with my gilts. I started them on Matrix on 3/25. Last dose was 14 days later on April 7. 2 of the gilts came in standing heat Wed and Thur this week as expected. Last gilt shows no signs at all of coming in. We've had a teaser boar here since the day they came off Matrix. All gilts have had physical contact with him twice a day to heat check. Today is day 7 after completing Matrix and still no signs of heat in this particular gilt. We know for sure this would have been her 3rd confirmed heat cycle. Any suggestions to get her in heat? We have some PG600 that we reconstituted on March 3 for initial shots for 2 gilts. There's 3 doses left, but bottle says only good for 24 hrs once it's made up. Tried to order more, but it's on back order everywhere and no one around here has any either. Does anyone know if it might work if we used what we made up back in March? Or, any other ideas to get her in heat? Semen shipment coming today.