Can a cat be happy with a 100% indoor existence?  Absolutely!  In fact, there are many reasons to keep your cat indoors.

• Outdoor cats are at risk of being hit by cars.  It is a myth that cats are naturally "road smart."  They also risk being attacked by dogs and wildlife.
• Cats that are let outdoors risk injury from other, more aggressive cats.  They are far more likely to contract Feline Leukemia (fatal and contagious to other cats), Feline Immunodeficiency Virus (fatal and contagious to other cats), Rabies (fatal and contagious to humans), and Upper Respiratory Infections (very common and very contagious to other cats) as well as many other diseases.
• Parasites such as fleas, ticks, intestinal parasites, heartworm, and bot flies run rampant in outdoor cats.
• Anti-freeze, rat poison, chemical cleaners, and fertilizers are all lethal to cats if ingested.  Anti-freeze has a sweet flavor, and many rat poisons are put into meat as bait.  These are fatal, tasty "treats" for a cat.
• There are people who do not like cats and think nothing of hurting them intentionally.  Some people steal or buy cats to train dogs to be aggressive for fighting purposes.
• Unaltered outdoor cats are the most common contributors to unwanted feline pregnancy. Every year millions of cats are euthanized because there are too many cats and not enough homes.
• Outdoor cats can cause property damage by territorial spraying and scratching.  Cat fights are very loud and disturbing.  Many outdoor cats use a child's sandbox as a litter pan.
• Many municipalities have leash laws for cats which means they cannot legally be outside unless leashed and attended by the owner.

Just because your cat seems bored inside, that doesn't mean she needs to go outside, only that you need to liven up her environment.  Interactive play (with a fishing pole toy or laser pointer) for 15-20 minutes, twice per day, will go a long way towards keeping your cat happy.  Felinestein (see Cat Resources) is full of suggestions to keep a home-alone cat happy.

For a cat who constantly cries to go out, it may be useful to have a scheduled time for the cat to go outside with you.  Since it is not safe (and often illegal) for a cat to be outside unattended, get a leash and a good harness.  A harness is better than a collar because many cats pull on the leash and a harness will put the pressure on the cat's shoulders rather than her neck.  It sometimes takes awhile for a cat to accept a harness and leash so be patient and go slowly when introducing this.  It is also important to have a scheduled time to take the cat out.  If she knows that she gets to go outside for a half-hour at 7:30am and 6:00pm, the cat will be less likely to try and bully you into taking her out at 4:30 in the morning.

For "door dashers" (cats that shoot out the door every time it's open), keep a container of treats near the door, and every time you leave, get the cat's attention and throw a treat on the other side of the room.  In time, you'll have taught your cat that when you are at the door, there is a treat on the other side of the room.

Regardless of whether your cat is 100% indoors, or sometimes goes out for walks on a leash, it is absolutely critical that you put a collar and tags on her and microchip if at all possible.  Cats that are lost without identification have a much, much smaller chance of being returned to their owner.  Tragically, far too many owners feel that their cat doesn't need a collar and tags and/or microchip because she never goes outside.  Exclusively indoor cats DO get out.  Animal shelters everywhere are loaded with cats that obviously belong to someone (they are neutered and/or declawed) that have no ID.  And, unfortunately, very few of these cats are claimed by their owners.