Keep in mind the prices I will let you know of are located in Paceras current market. We're in December and this event is during Valentines day. Pacera has been in Tibia since 2004 and is NON PVP. I know to profit off of this event you need to make sure you have multiple characters logged off near where she spawns (its what I do) to take advantage of some of the items that you just get once per year. You need to sell the items later in the year but not too close to Valentines Day. I'd say Summertime is perfect because Summerlove of course! There's some items she sell that aren't worth buying to profit off of so I'll just list the items I recommend.
Located in Greenshore village on Valentines Day.
Crimson Roses are 15 gps each from Valentina. Market avg price in Pacera 400 gps currently.
Heart Backpacks are 500 gps from Valentina (Once per year by saying hi, heart backpack, yes) Market avg price in Pacera 20,000 gps currently.
Sweetheart Rings are 500 gps from Valentina. Market avg price in Pacera is 900 currently.
Truelove teddy 1000 gps from Valentina (Once per year by saying hi, truelove teddy, yes) Market avg price in Pacera is 13,500 currently.