Despite The Sims series of games being rated ESRB Teen (13+), the "sex" in the games is very tame. The game doesn't even call it "sex", only "WooHoo" & the act of copulation is typically censored by a pixelation blur (which generally kicks in when a Sim is in a "personally sensitive" situation... like using the toilet [as nobody really wants to see that] & bathing [when the sim removes their clothes prior to entering the tub / shower]). The only time it would get EXTREMELY uncomfortable is if somebody installs the nudity mod (which removes the pixelation censorship blur) or the NSFW "WickedWoohoo" mod... which can easily increase the rating to Mature (17+), but these mods are outside the control of EA, Maxis & the ESRB / IARC
Your daughter has probably see more stuff on TV or even in your own house (depending on your family's privacy standards) than what she'll see in the game. Your daughter will eventually have two adult sims that are in love "WooHooing" it in-game, even if she doesn't actively trigger it. If two sims are in love with each other AND free will is enabled, the game's AI can make the decision to have those sims "WooHoo" on their own without your daughter's doing anything & may not catch it in either sim's action line (as you can queue up to 9 actions at any given time for a sim) to stop them. This is typically how those sims will have a child to progress the family tree & the family bloodline (unless it's a gay couple, which The Sims does provide the option to adopt a child as the alternative).
I do respect parents & guardians who actually take the time to do some research in games & ratings in order to determine what you believe is acceptable for them. While I don't have any children myself, I will restrict access to parts of my game library from my nephews, younger relatives & children of friends based on the content of the game... where I tend to be strict with the GTA series (which is clearly ESRB M & tends to push the boundary for the AO rating... which is considered the "Kiss of Death" with retailers) due to various mature content within the series. I'm a bit more relaxed with the Dark Soul series (which gets the ESRB M rating on combat violence more than gore) & the Saints Row series (while ESRB M as well, has a parody slant compared to the GTA series). Games rated with ESRB T typically gets the green light with me. HOWEVER, these lines are based on how mature I feel the person asking is & if their parents are OK with it. If their parent(s) are OK with the games where I'm on a bit on the fence, I'll let them play it.
Hope this sheds some light on the subject.