Opinion: Shannan’s Actions After Coming Home 
Could it be that when Shannann got home, after taking off her flip-flops and leaving her suitcase by the stairs, she went to her office to slip her purse inside so she could get all her receipts from the trip squared away. I’m sure she had the thought of the dinner transaction Chris had made on her mind too. It could have been possible Shannann did decide to take a shower, hence the T-shirt and underwear she was wearing and Chris used that time to go into the girls rooms. This would give him ample time to complete what he set out to do and he could have attacked Shannann after she was done getting dressed and sat in the bed to check the girls in the monitor before going to bed.