Do you have any kind of schedule during the day? 6pm is late for an afternoon wake up. Only to be put down again at 7ish.
Is she closer to 4 months? Babies have a 4 month sleep regression, which would also explain her waking up 20 minutes later, she fell asleep in your arms, then she comes out of her first sleep cycle and wonders where her mum is.
You could try putting her down awake but sitting by her bassinet / cot and patting her on the tummy or rubbing her tummy, so she falls asleep where she's going to wake up. This way you are still with her, she can see, feel, hear and smell you there with her and you aren't leaving her to cry alone.
Me 31, He 34, DD 21 months, waiting for just 1 more to complete our family.